Primary finding
Probable cause
The pilot's improper mixture leaning procedure. Factor(s) were: the disconnected ignition lead, dark night conditions, unsuitable terrain and the fence.
Investigator assessment
Analysis narrative
During cruise flight the engine began running rough and the pilot's corrective action was to apply full throttle and lean the mixture. He attempted to divert to an airport short of his destination and shortly thereafter he executed a forced landing under dark night conditions. The aircraft impacted a fence while passing over rough, obstructed terrain during the forced landing. Post crash examination revealed the #2 cylinder upper spark plug lead disconnected and evidence of detonation with a hole burned through the #2 piston head.
Source record
Factual narrative
On May 19, 1994, approximately 0303 hours Pacific daylight time (PDT), a Cessna 150L, N6747G, registered to and being flown by Thomas F. Hinckley, a certificated private pilot, was destroyed during a forced landing following a power loss while in cruise. The aircraft crashed approximately one mile west of the Rio Linda Airport, Rio Linda, California. The pilot was seriously injured. Visual meteorological dark night conditions prevailed at the time, and no flight plan had been filed. The flight, which was personal in nature, was to have been conducted in accordance with 14CFR91, and originated from Auburn, California, and was destined for Hayward, California. While receiving traffic advisories, the pilot reported that he had a rough running engine and was given vectors toward Natomas Airport. Radar contact was lost at 0303 hours. FAA onsite examination revealed that the aircraft had struck a fence, missing several other fences, railroad tracks and a power line before coming to rest against an upsloping embankment (refer to photograph 1). Additionally, fuel was found within the aircraft. Several unsuccessful attempts to contact the pilot were made and the last NTSB Form 6120.1/2 mailed certified to him was returned stamped "Moved, left no address" (see attachment). Post crash disassembly and examination of the aircraft's Continental four cylinder O-200-A engine by the participants revealed that the right magneto failed to produce a spark at lead number three. The ignition harness was tested and the number three lead was found to be open near the spark plug terminal which connects to the number two cylinder upper spark plug. Additional examination revealed a hole burned through the aluminum number two piston (refer to photographs 2/3) and aluminum particles contaminating the oil filter screen. Mr. Michael J. Grimes, representing Teledyne-Continental Engines, reported that pilot Hinckley indicated that "the engine was running rough, as though it had a fouled spark plug" and the pilot "then applied full throttle and leaned the mixture in an attempt to clear the perceived fouled plug" (refer to Powerplant Inspection Report attached). -